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How to Recycle HDPE Plastic the Easy Way

About: Come spend some time in the shop. I'm a hobbyist woodworker and professional computer geek in Northern California. I guess my projects will vary widely, and I have no clue what I plan to make next...
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After spending 2 hours cutting up a single milk bottle with kitchen shears, I knew I couldn't do it again.

I felt like a late night infomercial and may have actually uttered the phrase, "There has to be a better way!"

Turning old milk jugs and bottle caps into useable stock for making. In this short video I process a 2 milk bottles and about half a dozen bottle tops into a 1 1/2" x 3" x 5" turning block.

You could just as easily press this into sheet material for use in box inlays or scroll saw art. The possibilities are endless. The total processing time was under an hour from bottle to blank! Less than waiting for a glue up!

I'm curious if the plastic pieces scratched up the container at all. I honestly don't know if my husband would have survived doing that to my Vitamix!That said, I've been tempted to put non-food items into my Vitamix container as well, so I'm considering buying a second container if I can find a used one somewhere at a price I'd be willing to pay.

Every workshop needs its own vitamix...in my opinion...wish they weren't so expensive. But the good news is that you can often pick up a blender at a rummage sale for a couple of bucks. And if you take out the guts, they're mostly recyclable.

Polymers seldom melt sufficiently to consolidate without some compression. Kludge77 did the right thing by softening then pressing into a mould. If you just heat polymers for a long time and/or very high temperature you will get massive decomposition (yellowing) before they melt into a solid block.

Time is an issue, however most types of HDPE in small enough granules will join without compression. As I said elsewhere in the comments here I would actually recommend experimenting with a temperature range of 400-450F as that is the temperatures we use at my work to get the plastic to a nice light consistency without burning for cleaning it from metal tooling. The process uses high pressure compression and a temperature profile starting at around 330F and ending in the range of 350-365F. This lower temperature for the process allows for better surface appearance of the pressurized plastic and quicker cooling for the industrial process, but for creating "ingots" that cool at room temperature over a non-specified "cycle time" it would not be an issue. You wouldn't expect to see any decomposition of HDPE at 450F until molten at an extended time frame of maybe 20 or 30 minutes. Maybe even longer than that.

Yes HDPE powder can be sintered as low as 130C depending on grade. One of the research projects I worked on involved developing sintered polyolefin prosthetics. Sintering provides an open pored structure and this porosity weakens the material mechanically. I am sure that most uncompressed sinters would not survive lathe work. Moreover the porosity is very dependent on the polymer particle size. Roughly stacked polymer chips would produce a poorly sintered structure.

Sintering density is improved with elevated temperature and time. Polymers are good thermal insulators and getting the heat to penetrate to the centreof the powder of a large enclosed mould can take a very long time. Often hours not minutes. The outer layer is subjected to the full time and temperature. In our work we found the manufacturers decomposition temperatures to be very optimistic.

I once made an experimental series of consolidated sintered blocks (~150mm cube) using a range of conditions up to 250C and up to 4 hours, easily eclipsing the conditions you suggest. Every reasonably undecomposed sample turned out with only a consolidated skin ~2-3cm thick, the centre particles were still free flowing. I eventually achieved marginal success by repeatedly pulling the hot mould out of the oven and standing on it and then returning it to the oven. i{^_^}

BUT it does depend on what you call acceptable mechanical strength, density and decomposition; the medical standards for prosthetics are very strict. If what you made didn't fall apart; smell really bad; or end up in a child’s mouth it could be acceptable for some applications.

you will have to flip it once or twice so all the air trapped inside gets pushed towards the surface. The smaller tins (the rectangular ones) work best and punch a hole or two on top to vent the gas it lets off. For some reason placing large strips on the bottom and then adding smaller cut pieces keeps it from burning or getting that brown edging. Hope it helps...

I would like to make a sheet that could be rolled into a cone shape to make a cyclone dust separator similar to the Dust Deputy. Maybe starting by cutting and flattening 5 pound whey protein containers, then somehow joining them into a larger sheet.